"The Secretary-General welcomes the Security Council's adoption of a resolution demanding a cessation of hostilities throughout Syria for at least 30 days," Stephane Dujarric, Guterres' spokesman, said in a statement on Saturday, Xinhua news agency reported.

"The Secretary-General stresses his expectation that the resolution will be immediately implemented and sustained, particularly to ensure the immediate, safe, unimpeded and sustained delivery of humanitarian aid and services, the evacuation of the critically sick and wounded and the alleviation of the suffering of the Syrian people."

The secretary-general reminds all parties of their absolute obligation under international humanitarian and human rights law to protect civilians and civilian infrastructure at all times. Similarly, efforts to combat terrorism do not supersede these obligations, it said.

Resolution 2401 was adopted unanimously by the Security Council on Saturday after two weeks of tough negotiations against the backdrop of escalating violence in the country, particularly in Eastern Ghouta, the last major rebel enclave near Damascus.

The resolution demands an immediate cessation of hostilities for "a durable humanitarian pause for at least 30 consecutive days throughout Syria" to enable the safe, unimpeded and sustained delivery of humanitarian aid and services and medical evacuations of the critically sick and wounded.

It demands that, immediately after the start of the cessation of hostilities, all parties shall allow safe, unimpeded and sustained access each week for UN and partners' humanitarian convoys, including medical and surgical supplies, to all people in need in all parts of Syria, in particular to hard-to-reach and besieged locations.

It further demands that, immediately after the start of the cease-fire, all parties shall allow the United Nations and its implementing partners to undertake safe, unconditional medical evacuations, based on medical need and urgency.

The resolution also demands the immediate lifting of sieges on populated areas, including Eastern Ghouta.